One type of earth boring bit utilizes cones that are rotatably mounted to bearing pins of the bit body. The cones have cutting elements on their exteriors. As the bit rotates, the cones rotate to cause the cutting elements to disintegrate the earth formation. The cylindrical portion of bearing pin and cylindrical cavity of the cone define a journal bearing. Thrust bearing surfaces are located between flat portions of the bearing pin and cone cavity. The bearing spaces between the cone and bearing pin are filled with a lubricant. A pressure compensator equalizes pressure of the lubricant with the hydrostatic pressure on the exterior. A seal assembly seals the lubricant within the bearing spaces.
A variety of seals have been employed in the past. One type of seal uses metal-to-metal sliding contact. The seal assembly has a stationary metal ring and a rotating metal ring with the rotating ring rotating with the cone. The faces of the rings slidingly engage each other. The seal assembly has an elastomeric member that urges the rings in engagement with each other.
The journal and thrust bearings comprise metal surfaces that slidingly engage each other. Inlays may be employed in areas of the bearing surfaces to enhance the life of the bearing. Various coatings and metallurgical treatments to the seal faces and bearings have been proposed. These coatings including metal films and diamond and diamond-like layers. These bits are often run to destruction. To obtain the longest possible life at a desirable rate of penetration, the seal assembly should not leak or fail and the bearings surfaces should not wear excessively before the cutting structure is worn out.
Though not to employed with earth boring bits in the past, one technique for enhancing seal and bearing life in general is to provide a pattern of micropores in one of the rotating surfaces. These micropores comprise small holes or dimples formed in a pattern throughout one of the sliding surfaces. Each micropore of the prior art type is symmetrical, having leading and trailing portions that are the same slope.